Just to be sure, we at Mashery consulted the good ol’ Merriam Webster, which defines currency as “something that is in circulation as a medium of exchange.” I still contend that an API is exactly that—if you can broaden your view on what’s being exchanged.

Take retail, where brand value was traditionally built on physical reach (brick and mortar). Today, with customers increasingly interacting with apps and devices, almost anything can be a storefront. And I’m not just talking about apps branded by retailers. Angry Birds is a potential storefront. So is almost any app and website. And the way retailers are reaching these new storefronts is through APIs.

What’s exchanged through a retail, or an eCommerce API?

Call it service for access.

You might not think of Citibank as a potential storefront for Best Buy, but thanks to APIs, that’s exactly what it is. Have you seen the TV ads for Citibank’s loyalty program? All of the electronic items redeemable for Citibank reward points are sold and fulfilled by BestBuy, through its API. You can even find out if an item is in stock at your local Best Buy store, without leaving the Citibank context. Again, the exchange here is that Citibank gets a valuable service (electronics retailing & fulfillment) in return for turning its accountholders into potential BestBuy customers.

Of course, the opportunities for API-enabled exchange are only going to proliferate. As we’ve all heard, there will be 1 trillion connected devices, not in some future generation but as early as next year. At the most recent SXSW, we surveyed attendees to find out which they would rather give up, their cell phones or their wallets. You guessed it: the wallets, by 10 to 1.

The post-website era of eCommerce is turning out to be not only multi-location networks and industry-wide ‘co-opetition’ but also a full-on embrace of social media and mobile access. That’s where our customers are. In what Bob Pearson calls ‘pre commerce’ in his book of the same name, he addresses the importance of influencing consumers every step of the retail experience. Applications are now an integral part of this lifecycle, helping to connect us to deals, recommendations and immediate gratification. And if you want a piece of the action, you’ll need to pay for it with access to your goodies. You’ll need, in other words, a method of exchange. You’ll need an API.